A conventional semiconductor structure includes a substrate, and a layer that is formed on the substrate, that has a (100), (110), or (111) crystal orientation, and that includes doped regions, in which field-effect transistors (FETs) may be formed. It is well known that an FET uses either electrons, e.g., an N-channel FET, or holes, e.g., a P-channel FET, for conduction. It is also well known that electrons have a high mobility along a certain direction, and that holes have a high mobility along another direction that is different from the direction, along which the electrons have the high mobility. The conventional semiconductor structure is disadvantageous in that, since the doped regions thereof have the same crystal orientation, an optimum mobility performance can only be obtained for either N-channel FETs or P-channel FETs that may be formed therein. It is therefore desirable to provide a semiconductor structure configured to optimize a mobility performance of both N-channel FETs and P-channel FETs that may be formed therein.